Fluid-structure interaction during the water entry of flexible cylinders

In this work, we experimentally study the water entry of flexible cylinders. Experiments are performed in free fall and we explore variations of the entry velocity by varying the drop height. High speed imaging is utilized to study the fluid kinematics, the pile-up evolution, the cavity formation, and the overall structural deflection. The impact dynamics is analyzed through accelerometers, whereby fibre bragg gratings (FBG) measure the punctual deformation at characteristic locations on the cylinder surface. A modal decomposition approach is utilized to reconstruct the overall structural deflection from the punctual strain measurements. The proposed reconstruction methodology is compared against high-speed images. Results show that during the water entry the cylinder mainly deforms in the direction of the hydrodynamic loading, whereby marked vibrations whose amplitude increase with the entry velocity dominate the dynamic response.